Attachment means for the superstructure above the core in a light water boiling reactor

ABSTRACT

In a light water boiling reactor, a superstructure comprising a steam treating unit and a lid for the moderator tank is arranged above the moderator tank and is detachable for the purpose of interchange of fuel. A shield substantially concentric with the moderator tank and having a greater diameter is attached to the tank in such a position that the upper end of the shield is at a level above the lid of the tank. The superstructure is fixed to the upper part of the shield by a detachable hook joint which transmits compressive force against the lid to force it against the top of the tank through rodlike supporting members.

United States Patent [72] Inventor Bengt Martin Sodergard [56] References Cit d swede" UNITED STATES PATENTS [2i] Appl. No. 704,938

2,806,820 9/l957 Wigner 176/54 [22] Filed Feb. 12, 1968 7 3,144,393 8/1964 Raber et al. 176/54 [45] Patemed 1971 3 150 053 9/1964 G Id t 1 l76/54 [73] Assignee Allmanna Svenska Elektriska Aktiebolaget 0 man 8 a Vasteras, Sweden Primary Examiner-Reuben Epstein [32] Priority Feb. 14, 1967 An0rneyJennings Bailey, Jr [33] Sweden [31] 2015/67 ABSTRACT: In a light water bolllng reactor, a superstructure comprising a steam treating unit and a lid for the moderator [54] ATTACHMENT MEANS FOR THE tank is arranged above the moderator tank and is detachable SUPERSTRUCTURE ABOVE THE CORE IN A for the purpose of interchange of fuel. A shield substantially LIGHT WATER BOILING REACTOR concentric with the moderator tank and having a greater 6Claims,3l)rnwing Figs. diameter is attached to the tank in such a position that the upper end of the shield is at a level above the lid of the tank. [$2] [1.8. CI ll7766//5847, The superstructure is fixed to the pp p ofthe Shield y a [5 I] In G21 c 15/16 detachable hook joint which transmits compressive force 50 Field otSureh 176/54, 53, '9 the hmugh rodllke supporting members. 55,56, 87

l I I9 I 1 l 4 I I8 6 U 5 l 2 l l r r T A l M l l PATENTED DEC 7 |97| SHEET 1 [IF 2 llll llllllllllllllll INVINTOR BENGT MART/N fopEQGAkD 9 BY W97 ATTACHMENT MEANS FOR THE SUPERSTRUCTURE ABOVE THE CORE IN A LIGHT WATER BOILING REACTOR BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to means for attaching superstructure above the core in a light-water boiling reactor.

2. Description of the Prior Art A nuclear reactor of the boiling light water type usually comprises a steel vessel in which a moderator tank is arranged and above this a steam-treating unit. The moderator tank contains the reactor fuel and is provided with a detachable lid to enable the exchanges of fuel which must sometimes be carried out. So that the lid can be removed leaving free access to the upper side of the moderator tank, the steam-treating unit consisting of steam separator and steam dryer must be able to be lifted out of the reactor. The steam separator is connected to the moderator tank by a number of pipes fixed in the lid of the moderator tank. The lid must be tightly closed on the moderator tank and must also be held by a certain force so that it is not lifted by the internal pressure in the moderator tank. In known equipment the lid has been fixed by means of bolts in a flange around the upper edge of the moderator tank. These bolts are thus placed rather far down in the reactor and are consequently not easily accessible. The fact that the steamtreating unit normally has at least as great a diameter as the moderator tank also contributes to impeding the loosening or tightening of the flange joint bolts from the top of the reactor. This is done by means of rods which of course must be longer the further down in the reactor the flange joint is arranged. It may even be necessary to pass these rods through the casing of the steam-treating unit in order to reach the bolts, which of course does not facilitate the operation of these.

SUMMARY OF THE INVENTION According to the present invention these disadvantages are avoided by arranging a shield with greater diameter than that of the moderator tank concentrically around this and, by means of intermediate members, fixing it in such a position that the upper edge of the shield is on a level above the lid of the moderator tank. The core superstructure is fixed to the upper part by means of a detachable flange joint absorbing upwardly acting force, which flange joint transmits its tensile force to the shield and through supporting members transmits its compressive force to the lid which is thus pressed against the moderator tank. Since the shield is moved up to a level above the lid of the moderator tank, the flange joint is moved nearer to the top of the reactor and the rods for tightening the flange joint from the top of the reactor can therefore be made shorter in comparison with known arrangements. Since, furthermore, the shield is made with a greater diameter than the moderator tank, the flange joint also has a greater diameter than in previously known arrangements. This means that said rods for manipulating the flange joint can pas outside the casing of the steam-treating unit and not, as in the known arrangements, be passed through the casing.

The shield is suitably connected to the moderator tank by means of radially positioned metal plate members which are so designed that they simultaneously form a centering control for the lid of the moderator tank during insertion. This is of course an advantage since positioning the lid can otherwise pose problems due to the fact that the upper edge of the moderator tank is rather far below the upper edge of the outer casing of the reactor.

According to one embodiment of the invention the other part of the flange joint comprises a number of holders, each having a bolt joint consisting of a nut and screw. The bolt joint is pivotably joined to a hook. Holder and hook are suitably designed so that when the bolt joint is unscrewed the hook is flush-mounted in the holder but comes into engagement position when the bolt joint is screwed up. The flange part arranged on the shield is provided with a suitable engagement for said hook.

The connection pipes between the lid and the steam separator may be designed so that they form support members and can transmit compressive forces. In certain cases this is a disadvantage and according to a particular embodiment of the invention this can be avoided by providing the lid with supporting members in the form of a number of separate pressure rods which transmit compressive forces to the lid from the part of the flange joint which is not permanently fixed to the shield.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is better understood with reference to the accompanying drawings which show an embodiment of the invention.

FIG. 1 shows a schematic section of a boiling light water reactor.

FIG. 2 shows the flange joint in more detail.

FIG. 3 is a detailed sketch of the holder and hook forming the flange joint.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, l designates the outer casing of the reactor. The moderator tank 2 with the lid 3 are arranged inside this outer casing. Above the lid is the steam-treating unit 4 consisting of the steam separator unit the steam separator unit 18 and steam dryer I9. 5 is the shield, the lower part being fixed to the moderator tank and the upper part forming a mounting for the flange 6 which is arranged to fasten the steam-treating unit 4 and lid 3.

The same designations are used in FIG. 2 as in FIG. I. It is also clear from FIG. 2 how the shield 5 is fixed to the moderator tank by means of radially positioned metal plates 7. Since the plates 7 are bevelled at the top towards the shield they form a centering control for the lid 3 during insertion. The edge 6 of the shield 5 is bent in in order to provide engagement for the hook 8. The hook is arranged in a holder 9 fixed to the steam-treating unit 4. A suitable number of holders 9 is arranged around the steam-treating unit 4. The hook 8 is operated by loosening or tightening the bolt 10 with the help of the tool 11. As is clear from the drawings it is possible to pass the tool 11 completely outside the casing of the steamtreating unit 4. This is because the flange joint 6 has now been moved nearer to the outer casing of the reactor clue to the insertion of the shield 5 with a greater diameter than the moderator tank 2. FIG. 2 also shows how compressive forces from the holder 9 are directly transmitted to the lid 3 by means of a rod 12. Such a rod 12 is suitably arranged for each holder 9.

FIG. 3 shows more clearly the design and function of the holder 9 and the hook 8. 5 still designates the shield, 4 the steam-treating unit and 9 the holder itself. In the holder the hook 8 is pivotably suspended in a bolt joint consisting of a screw 13 and a nut I4. The hook 8 is further provided with a projection 15 which is influenced by a spring 16 arranged in the holder 9. When the joint is loosened by turning the nut 14 with the tool 11 the hook 8 first moves downward under the pressure of spring 16 and thus moves out of engagement with the shield. When the nut 14 is loosened further the projection IS on the hook 8 meets the stop 17 in the holder 9 and the hook 8 returns into the holder 9. Thus the hook 8 cannot reengage when the steam-treating unit 4 is lifted up. After reinsertion of the steam-treating unit 4 and upon tightening of the joint the hook 8 moves into the engagement position,influenced by the turning of nut I4 and the pressure from spring 16. The joint is prestressed by continued turning of the nut. The prestress is limited by torque limitation of the tool 11. The nut is joumaled in a spherical seat which prevents the screw I3 from being flexurally stressed. The transverse force arising is absorbed in a contact surface between the eyebolt and a flat tongue on the nut seat. The thread surfaces should be extremely hard in order to reduce the risk of jamming. When choosing the material this is a requirement which is in opposition to the requirement for corrosion resistance. Relatively low surface hardness must therefore suffice and a certain amount of jamming will certainly arise in the thread surfaces. After repeated tightening and loosening, therefore, the thread surfaces will become uneven and the friction will increase. If a very strong jamming occurs in the thread the loosening torque momentum may be increased until the shaft of the screw breaks. As seen in FIG. 3 the shaft is the weakest point. The device is so designed that in such a case the hook 8, due to gravity and spring pressure, falls into what is its normal position when the screw is loosened. The hook 8 cannot fall down into the reactor. The screw unit is exchanged, for instance, behind a temporary stationary radiation shield in the reactor hall.

I claim:

1. Attachment means for a core superstructure arranged above the moderator tank in a boiling light water reactor, which superstructure comprises a steam-treating unit and a lid for the moderator tank and is detachably arranged to expose the upper side of the moderator tank for fuel exchange, characterized in that a shield substantially concentric with the shell of the moderator tank and having a greater diameter than the tank is attached by means of intermediate members to the tank in such a position that the upper edge of the shield is at a level above the lid of the moderator tank and in that by means of a detachable flange joint absorbing upwardly acting force the superstructure is fixed to the upper part of the shield,

which flange joint transmits its tensile force to the shield and through supporting members transmits its compressive force to the lid which is thus pressed against the moderator tank.

2. Attachment means according to claim 1, characterized in that the superstructure comprises a separate steam-drying unit to which one part of the flange joint is fixed.

3. Attachment means according to claim 2 characterized in that the supporting members comprise rods which are supported by the lid.

4. Attachment means according to claim 1, characterized in that the intermediate members fixing the shield to the shell of the moderator tank comprise radially positioned metal plate members which have means thereon to form a centering control for the lid of the moderator tank during insertion.

5. Attachment means according to claim 1, characterized in that the part of the flange joint fixed to the superstructure comprises a number of holders each having a bolt joint comprising a nut and screw and a hook pivotably joined to the bolt joint, and that the flange part fixed to the shield is designed to engage with said hooks.

6. Attachment means according to claim 5, characterized in that said hook is arranged to be flush-mounted in the holder when the bolt joint is unscrewed, but to come into engagement position when the boltjoint is screwed up. 

2. Attachment means according to claim 1, characterized in that the superstructure comprises a separate steam-drying unit to which one part of the flange joint is fixed.
 3. Attachment means according to claim 2 characterized in that the supporting members comprise rods which are supported by the lid.
 4. Attachment means according to claim 1, characterized in that the intermediate members fixing the shield to the shell of the moderator tank comprise radially positioned metal plate members which have means thereon to form a centering control for the lid of the moderator tank during insertion.
 5. Attachment means according to claim 1, characterized in that the part of the flange joint fixed to the superstructure comprises a number of holders each having a bolt joint comprising a nut and screw and a hook pivotably joined to the bolt joint, and that the flange part fixed to the shield is designed to engage with said hooks.
 6. Attachment means according to claim 5, characterized in that said hook is arranged to be flush-mounted in the holder when the bolt joint is unscrewed, but to come into engagement pOsition when the bolt joint is screwed up. 